Outdoor swimming pools are becoming more and more popular. However they need to be regularly cleaned to remove dropped leaves for example, and when not in use, they can lose heat very quickly from their exposed top surface. This can be overcome by covering the pool. Ordinarily this is commonly addressed by providing a retractable plastic or fabric cover which is typically provided on a roller adjacent to the pool, and when it is necessary to cover the pool, the cover is simply unrolled and pulled over the pool. Typically these covers are fabric and although they do successfully cover the pool thus minimising debris entry and heat loss, they do not permit the covered surface to be used in any other way, as they are simply too weak to bear any additional weight.